For many years the automotive industry has been faced with a problem in their silicone rubber based power train sealing gaskets called "weep". Weep occurs due to a temperature dependency of the swell of silicone rubber in engine oil. Swell describes the tendency of an elastomer in contact with certain fluids to change in linear dimensions, as a function of time and temperature, as the fluids are adsorbed into the elastomer matrix. Silicone rubbers swell more at higher temperatures (T.sub.2) than at ambient temperature (T.sub.1). Upon cooling the extra oil which is taken up in going from ambient temperature to higher temperature is expelled out of the material, forming weep, allowing oil to pass through the gasket.
Blizzard et. al in U.S. Pat. No. 5,739,192 teach polysiloxane copolymers produced by a Michael Addition reaction between polysiloxanes containing amine functional groups and acrylates having hydrocarbon containing groups. However, this patent does not teach a method of making alkenyl-functional poly(siloxane-acrylates) which are curable via free radical and hydrosilylation methods.
Lo et. al in U.S. Pat. No. 4,698,406 teach a curable two-part silicone composition comprising (i) an amine-functional polyorganosiloxane and (ii) acryl-functional polyorganosiloxane selected from acryloxy, methacryloxy or acrylamide-functional polyorganosiloxanes. Components (i) and (ii) of the composition cure by a Michael-type addition to form a solid polyorganosiloxane resin or elastomer.
Pendant methacryl-functional siloxanes have been prepared by reacting pendant aminosiloxanes with difunctional acryl compounds in a Michael-type addition reaction. See for example Lee et al. in EP Pub. No. 230,242, and Griswold et al. in EP Pub. No. 274,699. Siloxanes containing functional methacrylate groups have recently gained importance, because they may be cured by UV irradiation rather than by thermal initiation.
The object of this invention is to make poly(siloxane-acrylate) elastomers with reduced weep when exposed to engine oil and fluids in automotive power trains. Another object of this invention is alkenyl-functional poly(siloxane-acrylates) which are curable to such poly(siloxane-acrylate) elastomers. Another object is a method of making the alkenyl-functional poly(siloxane-acrylates) with pendant oxycarbonylethyleneimino-containing organic groups using a Michael-type addition.